What Air Pipe?

What air pipe should you consider for your air compressor? Looking for another way to plumb your compressed air? There is lots of information about this subject on this and other pages on thsi site.

Odds are good that a new, lower cost, DIY type air compressor will come with a low cost PVC hose. That hose will have a connector on one end, and a coupler on the other.

The PVC hose that came as part of one of my compressors was very hard to work with. The connector leaked around the barb when it was plugged into the compressor coupler. When the weather got cool I could not unroll it easily. It would not lay flat on the floor and I kept tripping over it. So I got rid of it the cheap PVC hose, and paid a bit more to acquire much easier-to-use rubber hose, one with male fittings on either end. I could then add the coupler and connector of choice, which I did, using better fittings than had come with the original PVC hose.

If you are plumbing up a plant with air mains and drop lines and such, what type of air pipe should you consider then?

What Air Pipe?

Industrial compressed air plumbing was, and continues to be built using black metal pipe. Many folks still use it as it is relatively cheap when lots of pipe is needed for a plant installation. And I suppose it is cheaper if a larger air main is needed. But...

Black Pipe Issues

Whether at home or in the plant, I personally would not select black pipe unless I absolutely had to. Despite the best efforts at drying the compressed air, some moisture will still condense in those pipes, and rusting will occur. In time, the rust scales will migrate to the air equipment and, along with the compressor oil, and air borne dust, more compressor-generated water foul up tools, valves and cylinders.

I might have to use black pipe if my air mains were going to exceed 2" in diameter. There are not too many other options in piping once you get that big.

Polyethylene Tube

For my home shop or for a small plant, I would first consider using polyethylene tube to plumb all the air lines.

Polyethylene tube is low cost, it is rated for industrial compressed air pressures, it is very easy to install, does not react with moisture in the compressed air and it has scads of different air fittings (link to fittings information on this site) to enable easy plumbing. Not to mention that you can buy it, rated for industrial pressures of about 300 PSI, almost anywhere plumbing goods are sold.

The problems with polyethylene tube are that if you need large volumes of air, you cannot get a tube large enough for high air flow, if you bend it, it tends to leave a permanent kink and a weak spot in the tubing, and it is not abrasive resistant, meaning you would not polyethylene tube as an air line to an air tool. Those air lines end up laying on the floor, and poly does not take well to being walked on or hand-trucked over.

Copper Pipe

In my opinion, after poly tube, the next best plumbing material for the home or small shop is copper pipe.

Yup, the same copper that is used to plumb the water lines.

If you have any experience with soldering copper is really easy to work with, has lots of fittings to convert from soldered copper to threads for installation into components, and it too, does not rust.

If soldered properly copper fittings and joints should never leak, giving the user potential to save the energy costs many other compressor owners waste to atmosphere through air line and fitting leaks. It used to be lower cost.

A drawback now is that copper prices continue to rise, making an all-copper installation quite expensive. And, if you cannot solder, installing leak free joints with copper can be a bit of an issue.

Rubber Hose

Next, consider using rubber hose, if you can get one large enough for your air lines.

Whether hung on the wall, running along the ceiling, or laying on the floor to be stepped on or hand-trucked over, rubber hose is resistant to abrasion, some of it is very resistant to chemicals in the working environment, and it plumbs around corners just fine.

If you need a tight elbow, a couple of gear clamps and a 90 degree barbed fitting sized to suit, and you are tight to the corner. Need more air line; the same scenario. A couple of gear clamps and a straight, male-to-male barbed fitting, and the hoses are connected.

There are some potential problems with hose.

Like polyethylene tube, rubber hose may have some size constraints if your air mains need to be larger than 3/4".

Rubber air hose festooned around the walls of the shop may not look as professional as you would like.

And, if you don't put the barbed fittings and gear clamps on properly, you will get air leaks. Inspect the fittings after a short while to see if a change in conditions in the plant has allowed any of those fittings to leak. Compressed air is the most expensive industrial energy form there is and you will not want to waste it.

Galvanized Pipe

On the air site, I did get many responses when asking folks about the use of galvanized pipe in air systems. Here is one response, sent in by Paul Pearce.

"I am a Millwright & here is what I think about galvanized pipe for compressed air systems. I judge galvanized piping as a totally wrong application that is doomed to failure.

I can't imagine how and why anyone would apply this type of weak and inherently flawed piping. It is weak because it is totally susceptible to corrosion, flaking, and pin-hole defects - depending on the skill with which it is dipped.

And once a pin-hole (or even smaller holes) has been established, the corrosion starts immediately. There is no way on this earth that anyone can guarantee that there is no defect or flaw in a given galvanization - hot-dipped or not hot-dipped.

And then there is the real hard issue of how does one inspect the surface that is really supposed to be doing the protecting : the internal pipe surface! To date I've never heard or read of anyone daring to state that the internal surface of a galvanized pipe can be safely guaranteed not to have defects or flaws - because it can't be inspected.

Most, if not all galvanized pipe is threaded. The moment it is threaded, the galvanization has been compromised and breeched. There is no longer any protection, since the galvanization has been stripped and removed at the weakest point - the threads! This methodology or system of ensuring corrosion protection for a pipe has all the ingredients for its own demise."

Paul is pretty clear how he feels about galvanized pipe for compressed air, and I tend to agree with his analysis.

Composite / Plastic Air Pipe

There are some companies that build a composite plastic piping system for compressed air. I know that this product is not approved for use in every state, province, or country, so check carefully.

I am against using PVC and CPVC plastic pipe for plumbing compressed air regardless of the source. As ambient temperatures rise, the pressure rating of plastic pipes drops dramatically, and may quickly fall below standard industrial compressed air pressures. Should the plastic pipe fail, rather than springing a leak, the plastic will shatter, sending shards in every direction.

I am saying do not use any plastic pipe for compressed air unless you contact the manufacturer of that plastic pipe, and get an approval in writing from them that they recommend the use of their pipe for compressed air. No letter? Do not use it!

Ultimately, with what pipe you use for your compressed air lines is up to you, your budget, your installation-skill-level, and how much air you need to your equipment.